The process gases used in the semi-conductor industry are usually toxic, corrosive, or even damaging to the ozone layer, or generate a strong greenhouse effect. The gases extracted must therefore be treated before any are expelled into the atmosphere, so that only relatively harmless gases are released.
Until now, process gases have mainly been treated in gas treatment assemblies at pumping system discharges. Consequently, such gas treatment assemblies must be designed and dimensioned to treat the entire pumping system outflow.
A first disadvantage of known gas assemblies units is their large size, which is necessary to treat the large outflow quantity. These gas treatment assemblies are therefore located elsewhere, in other words placed on a lower floor of semi-conductor production plants and connected to the process chamber via long and costly lines. The size of these gas treatment assemblies makes it impossible to install them near process chambers.
A second disadvantage is that the pumping system outflow contains not only the gases extracted from the process chambers, but also the purge gases that are introduced into the vacuum chain, between the process chamber outlet and the pumping system discharge. These purge gases, which are added to protect the pumping systems, disrupt the effectiveness of the gas treatment process and add further complications, leading to an additional increase in the size of gas treatment assemblies.
More recently, document U.S. Pat. No. 5,672,322 proposed a gas treatment system external to the pump that is not connected to the pump's discharge, but between two of the pump's successive stages, using bypass lines.
The gas treatment may in this way be improved as the harmful gases may be treated before their dilution by the purge gases in the pump's successive stages.
However, these bypass gas treatment systems between successive stages of the pump, which are only partially integrated with the pump, again present significant disadvantages, which are explained below.
In particular, with such a bypass gas treatment between successive stages of the pump, the operating of the pump itself is apparently degraded, as a reduction is observed in pumping capacity, pumping speed and vacuum performance. The pumping system is thus disrupted by the presence of the gas treatment system and more effective gas treatment is provided to the detriment of pump efficiency.